IMO Biofouling Guidelines 2023 (Biofouling Management Plan)


( At its 80th session, the IMO’s Marine Environmental Protection Committee adopted revised guidelines for the control and management of ships' biofouling to minimise the transfer of invasive aquatic species. The update to the 2011 Guidelines was undertaken to improve uptake and enforcement and to reduce the threat posed by invasive aquatic species to the well-being of the ocean.

As well as addressing the threat posed by invasive aquatic species the update of the guidelines recognises that an increased uptake and improved biofouling management supports improvements in a ship’s hydrodynamic performance and can be effective at enhancing energy efficiency – thus reducing greenhouse gas (GHG) emissions.
The guidelines feature some points of consideration regarding ship design and construction but are primarily focussed on operational considerations- namely the selection and installation of an antifouling system (AFS) and the re-installation, re-application or repair of an AFS as well as guidance on marine growth prevention systems (MGPS).

A focus on inspections

Biofouling inspections are elaborated on and the guidelines provide scope for inspections by organisations, crew or personnel who are competent to undertake such inspections. A fixed schedule for inspections is provided and is based on a ship-specific risk profile. This schedule takes into account performance monitoring undertaken by the ship but in general recommends:

  • Inspection frequency or inspection dates (or date ranges) for in-water inspections during the in-service period of the ship should be based on the ship-specific biofouling risk profile, including inspection as a contingency action, and specified in the Biofouling Management Plan (BFMP). The BFMP should also specify management actions to be taken when biofouling is identified during inspections (eg cleaning), including changes to inspection frequency
  • For ships not undertaking performance monitoring, the first inspection date should be within 12 months of application, reapplication, installation or renewal of the AFS to confirm their effective operation
  • Where monitoring indicates that the AFS is not performing effectively soon after application, reapplication, installation or renewal (eg increased fuel consumption), an inspection should be carried out to confirm the condition of the AFS and level of biofouling as soon as practical or possible, in line with the BFMP and contingency action plan. If adequate performance of the AFS is observed through monitoring, the inspection could be conducted up to 18 months after application, reapplication, installation or renewal, noting that such monitoring may not reflect the level of biofouling in all niche areas
  • Subsequent inspections should occur at least every 12 to 18 months and may need to increase in frequency to confirm the continued effectiveness of an ageing or damaged AFS. In-water inspections should seek to coincide with existing subsea operations (eg underwater inspections in lieu of dry-dock or any other in-water inspections), including any unscheduled subsea operations
  • If no AFS is installed in areas of a ship and no other measures are undertaken such as in-water cleaning or propeller polishing, then inspections should occur more frequently.

Determination of fouling rating and subsequent actions

The aim of an inspection is to determine a biofouling rating based on the type and extent of biofouling as well as the condition of the AFS and the functioning of any MGPS. The determined rating scale then provides a recommendation on the type of cleaning that should take place should biofouling of a certain rating be present.

  • A fouling rating of zero is given when there is no fouling
  • A fouling rating of one is given where submerged areas are partially or entirely covered in microfouling. Metal and painted surfaces may be visible beneath the fouling. Here proactive cleaning may be recommended
  • A number of different fouling ratings are defined from light macrofouling (presence of microfouling and multiple macrofouling patches) all the way through to heavy macrofouling (large patches or submerged areas entirely covered in macrofouling). In all these cases reactive cleaning with capture is recommended and should achieve a fouling rating of less than or equal to one
  • In all cases of macrofouling it is also recommended to shorten the interval until the next inspection
  • If the AFS is significantly deteriorated, dry-docking with maintenance and reapplication of the AFS is recommended.

The guidelines also provide updates to information to be included in a biofouling management plan and biofouling management record book.

The 2023 Biofouling Guidelines can be downloaded below:





Source: IMO






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